This study plans to study hormone response (cortisol and the protein which binds it, glucocorticoid receptors) and immune response (cell-mediated and antibody responses, cytokines and lymphocytes) which regulate the body's response to stress and illness, to a man-made hormone called dexamethasone in posttraumatic stress disorder (PTSD). PTSD has been shown to have abnoramlities in the hormone and immune measures that we plan to study.